Eductors are widely used in pumping liquids and gases because they are relatively simple to build and operate, and because they are largely free of mechanical breakdowns. An eductor pump essentially comprises a venturi element through which a driving fluid is passed at an appropriate flow rate to create a reduced pressure space around the venturi outlet. A feed fluid, which it is desired be pumped, is permitted to flow freely by gravity or by application of pressure, to the reduced pressure space where it is inspirated and propelled with the driving fluid as a mixture therewith. The pumping efficiency of the eductor will depend on the driving liquid flow rate, the viscosity of the driving liquid and the feed liquid, the size and shape of the venturi element and other factors, all of which is known to those skilled in the art.
Recently, W. J. Haggard U.S. Pat. No. 4,298,018 disclosed use of an eductor pump for pumping viscous liquids, such as a detergent slurry, from a storage container. The feed liquid inlet at the bottom of the pump is continually open so that feed liquid can flow in and out. This is considered desirable since the pump is to be used on an intermittent cycle with water as the driving liquid. During intermittent pumping, detergent slurry is pumped by use of water flowing through the venturi element. Pumping is then stopped for a short time so that water mixed with detergent slurry can flow out the pump lower end and dilute the slurry in the immediate vicinity. Such diluting is effected during a pumping cycle as well as after a cycle is effectively completed.
The eductor pumping method of W. J. Haggard, while possibly of value for pumping viscous slurries, is generally unsuitable for pumping low viscosity slurries, suspensions, solutions or pure liquids where dilution in the container of the feed liquid is unnecessary or undesirable. A need accordingly exists for an improved eductor pump which will bar feed liquid which enters the pump body from flowing outwardly through the feed liquid inlet, whether or not diluted by driving liquid.